Re: [PATCH] drm/i915: Wait for vblank after register read

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 20 Apr 2018, Mika Kahola <mika.kahola@intel.com> wrote:
> On Thu, 2018-04-19 at 17:09 +0300, Jani Nikula wrote:
>> On Wed, 18 Apr 2018, Mika Kahola <mika.kahola@intel.com> wrote:
>> > 
>> > When reading out CRC's we  wait for a vblank on
>> > intel_dp_sink_crc_start()
>> > function. When we start reading out CRC's in intel_dp_sink_crc()
>> > loop we
>> > first wait for a vblank yielding that all in all we end up waiting
>> > two
>> > vblanks on the first iteration round. Therefore, let's move the
>> > intel_wait_for_vblank() as the last routine that we do in an
>> > iteration loop
>> > in intel_dp_sink_crc().
>> > 
>> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103166
>> Umm, do the CI failures in the bug really use sink crc, or are they
>> rather about pipe crc?
>> 
> The bug is more on pipe crc. This just caught my attention while I was
> looking into these bugs. 

I think the practice we've adopted is,

Bugzilla: <bug that this patch should fix>

References: <bug or something else that this patch is related to>

> Was there a reason why we need to wait two vblanks here before running
> the loop?

I can't remember by heart. I'm not sure if it would make more sense to
remove the vblank wait from intel_dp_sink_crc_start() instead. Even with
your patch, there'll still be an extra vblank wait, you just move it to
a different place.

BR,
Jani.


>
>> BR,
>> Jani.
>> 
>> 
>> > 
>> > Signed-off-by: Mika Kahola <mika.kahola@intel.com>
>> > ---
>> >  drivers/gpu/drm/i915/intel_dp.c | 5 +++--
>> >  1 file changed, 3 insertions(+), 2 deletions(-)
>> > 
>> > diff --git a/drivers/gpu/drm/i915/intel_dp.c
>> > b/drivers/gpu/drm/i915/intel_dp.c
>> > index 62f82c4..6eb97fa 100644
>> > --- a/drivers/gpu/drm/i915/intel_dp.c
>> > +++ b/drivers/gpu/drm/i915/intel_dp.c
>> > @@ -3972,13 +3972,14 @@ int intel_dp_sink_crc(struct intel_dp
>> > *intel_dp, struct intel_crtc_state *crtc_s
>> >  		return ret;
>> >  
>> >  	do {
>> > -		intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
>> > -
>> >  		if (drm_dp_dpcd_readb(&intel_dp->aux,
>> >  				      DP_TEST_SINK_MISC, &buf) <
>> > 0) {
>> >  			ret = -EIO;
>> >  			goto stop;
>> >  		}
>> > +
>> > +		intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
>> > +
>> >  		count = buf & DP_TEST_COUNT_MASK;
>> >  
>> >  	} while (--attempts && count == 0);

-- 
Jani Nikula, Intel Open Source Technology Center
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